BEHAVIORAL PHENOTYPING CORE (BPC) The NIH BACPAC initiative is designed to ?generate new knowledge regarding phenotypes, endotypes, mechanisms, diagnostics, trial outcomes, and therapeutic responsiveness . . . in chronic low back pain (cLBP). This proposal, to lead a Mechanistic Research Center (MRC) as part of the broader BACPAC initiative, includes a Research Core that takes advantage of a multidisciplinary team at University of Michigan which has been characterizing and studying a wide variety of chronic pain conditions for over 20 years. Members of this Core have either led or participated in the design and conduct of large clinical and network based projects that have required clinical and behavioral phenotyping such as the Department of Defense (DoD) studies of Gulf- War Illnesses, the NIH/NIDDK MAPP initiative, the NIAMS CORT, and registration trials for industry. The co- Directors and members of this Core have also been involved in the development and validation of PROMIS derived measures for chronic overlapping conditions which includes cLBP. For this application, the Behavioral Phenotyping Core (BPC) faculty have designed a comprehensive phenotyping battery that incorporates multi- domain self-report questionnaires (derived largely from PROMIS, the NINDS common data elements, or recommendations from the NIH Chronic Low Back Pain Task Force) along with multi-modal assessment strategies such as ambulatory monitoring (e.g., actigraphy and ecological momentary assessment (EMA)) and functional capacity examination (Specific Aim 2). Our phenotyping occurs at baseline and longitudinally throughout the project and corresponds with the effort of the Neurobiological Phenotyping Core (NPC) (Specific Aim 3). The BPC team has also contributed to the design of the research project and selection of relevant primary and secondary outcomes for the study including a priori mechanistic hypothesis-based outcomes specific to the purported actions of each intervention. In order to support the integrity of the research project, this Core also designed indices of treatment fidelity, adherence, credibility, and expectancy (e.g., Specific Aim 1). Finally, the BPC is eager to contribute to the broader BACPAC initiative by having our well- characterized cohort of cLBP patients serve as a resource for the larger NIH BACPAC initiative and by contributing scientific expertise, research methods, and leadership to BACPAC.